The focus of the proposal is the continued characterization of genes and gene products that mediate epithelial morphogenesis. The morphogenesis of imaginal discs of Drosophila melanogaster serves as a model system. Imaginal discs are epithelial precursors to the appendages and much of the body structure of the adult. The insect steroid hormone, 20-hydroxyecdysone, induces disc morphogenesis under in vitro conditions in which subsequent disc development is blocked. The morphogenesis of discs is under the control of an ecdysone-responsive trans-acting regulatory gene referred to as the Broad-Complex (BR-C). Accumulating evidence suggests that cell surface components play a key role in disc morphogenesis. By seeking genes with ecdysone-dependent expression that putatively encode cell-surface proteins, or that are regulated by the BR-C we have identified seven genes that appear to mediate disc morphogenesis. We have also identified a major cell-surface glycoprotein that is altered during disc morphogenesis. We propose a thorough genetical, molecular, cellular and developmental study of several of these genes and their products so as to elucidate their roles in morphogenesis. Because of the evolutionary conservation of key cell surface and cytoskeletal components, it is likely that these Drosophila genes will have homologs that mediate epithelial morphogenesis in other animals, including vertebrates.